Studies in the Physical Ecology 
of the Noctuidae 


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A THESIS SUBMITTED TO, THE FACULTY OF THE GRADUATE 
SCHOOL OF THE UNIVERSITY OF MINNESOTA 


BY 


WILLIAM CARMICHAEL COOK 


IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE 
DEGREE OF DOCTOR OF PHILOSOPHY 


49.252 


MINNEAPOLIS 


CONTENTS 

Page 
IAEF OCU CEG Recah oye us trace cee er es Sree te eee ic ear ake ea RR apne tee 5) 
Definitions Ofc terms sje Ve ide am eer nel a is ay We abi ery to 3 
Literature eso Ayo EG i eek Oe eat cae tinier on re rena he Co eee ae «| 
Littesrat Stidy pursued 4.4 vy Boteee aeete the we cen Roe ene nee eee ee 6 
Meth ods etisedsJivc% rotecyet somata Caan tae Gee earn ae ene a, Seer 6 
Comparative climatology of Minnesota and Montana. 3. ..7-.> a.2-. ee 7 
General ecology of the Noctuidae of Minnesota and Montana... ..:....... 9 
Larval habits, oc. «0 sce sacs ate eirad he. ele Oe eee Ree ec ee 10 
Acdtilts habits cio obs. 5 iat. G teenies Bie cee aria oat en gate ea NI an 11 
Physical-ecology .of ammatures Stages cre ust card eee ee eee 12 
Laboratory studiéss.< sews t 2. oe dente tees ce ae ne ‘We 
Soilmoisture “relations vou oa ach ler eens eras et ae en re 12 
‘Léemperature: relations. senate er eee eee ee A Alig ae 15 
Fieldt and ‘statistical sstindiese . spon. ter ns aes arenes reac 16 
Conclusions 4... eet ee eee Fah esis Wi AL Oe: iE ae, ae En ee 29 
Meteorologicalerelations ofsadult moths: sores 5 arene ote ea er eee 30 
Methods ‘of-statisticalanalysisen 4 ngs eet ae tate eee 34 
CoriclusSiGng Seo. AS Nn oie ee anal ose oe cee need 19h eee eR aa 36 
Bibliography: So pclae. aikts oo ooo Seatac St een ae et 37 

ILEVST RATIONS 
Page 
Plates ts Comparative sclimatolog yess ans ceee rere aes tre ee AY 
Plate-1 ll Demperaturerelationes..- nce ne ee ee Renee Wi 17 
Plate III. Meteorological relations of Cirphis untpuncta.....+. o..ti.....- 23 
Plate 1V 2 Climatological srelations;0f.N Octuidae seam tes ees 24 
Plate ,_V.=) Meteorological relations of sadulemoti= recente een ee 33 


re ee + FeLt11.+2.2_e oO Ce 


on 


era Cee 


STUDIES IN THE PHYSICAL ECOLOGY 
OF THE NOCTUIDAE 


3y W. C. Cook 


INTRODUCTION 


This paper gives the results of an attempt to determine the effects 
of the various meteorological factors on the distribution, seasonal 
abundance, and activity of certain species of the insect family 
Noctuidae, which are commonly classed as cutworms and army worms. 
As yet the studies include but few species, but the results so far 
obtained seem of fundamental importance, and the methods used, altho 
somewhat novel to entomologists, are applicable to the solution of 


many similar economic problems. 


DEFINITIONS OF TERMS 

Physical ecology may be defined as the study of physical factors in 
their relation to the ecology of a species. Such factors are light, heat, 
and moisture as opposed to associational factors such as parasites, or 
chemical factors such as food relations. The study of these physical — 
factors under field conditions comes within the realm of meteorology, 
and the factors themselves fall into two general classes, weather and 
climate. Prof. J. Warren Smith (’20, p. 1)’ makes the following 
comparison of these groups: 

“Weather is the condition of the atmosphere at a definite time. It 
includes all the phenomena of the air that surrounds us, such as pres- 
sure, temperature, moisture, wind, and the like. 

“Climate deals with the averages and the extremes of the weather 
that prevail at any place. Thus it will be seen that weather relates to 
time and climate to location.” 


LITERATURE 

Most of the previous work on insect forms has been confined to 
laboratory experiments under controlled conditions or to the drawing 
of general conclusions from a superficial study of field data, without 
subjecting the data to any form of mathematical analysis. This is the 
case in the early development of any branch of science, the qualitative 
form preceding the quantitative. Our entire knowledge of quantita- 
tive physical ecology may be said to consist of a few definite laws of 
growth deduced from laboratory experiments, and a few broad 
generalizations on the effects of climate on animal and plant distribu- 
cited at the end of 


1Datés in parentheses refer to titles in the list of literature 


the paper. 


4 1 BCANICALISUELETIN 212 


tion and activity. Some of the more important of these deductions 
are worthy of mention in connection with this specific problem. 

Working under controlled laboratory conditions, Sanderson and 
Peairs (713) determined that the effect of temperature upon insect 
growth might be represented by a rectangular hyperbola of the 
formula XY=A?’, A being a constant, called by them the thermal 
constant, X being the temperature, and Y being the time of develop- 
ment. By plotting X against || the plot becomes a straight line which 
intersects the temperature axis at the point === (); Ol pOiit Ol ato 
growth, which they called the developmental zero. The quantity : 
they have termed the index of development, and it represents the part 
of total growth accomplished in one day. In most cases in which this 
method of plotting was used, it has been found that the relations out- 
lined above hold true for the portion of the temperature range which 
is approximated under field conditions, and that the developmental zero 
found mathematically is a very close approximation to the point of 
dormancy under field conditions. 

W. D. Pierce (16) showed that the effect of temperature com- 
bined with humidity was to change the developmental zero of Sander- 
son to an elliptical curve whose foci were the optimum condition, and 
that Sanderson’s curve of growth was a zone inside of this ellipse. 
Any cross-section of this zone, parallel to the humidity axis, gave a 
hyperbolic temperature curve, as before. 

Studying the distributional data obtained by the United States 
Biological Survey, C. H. Merriam (’98) formulated a general law of 
animal and plant distribution, as follows (798, p. 54). 

“Investigations conducted by the Biological Survey have shown that 
the northward distribution of terrestrial animals and plants is governed 
hy the sum of the positive or effective temperatures for the entire sea- 
son of growth and reproduction, and that the southward distribution 
ts governed by the mean temperature of a brief period during the 
hottest part of the year.” 

By the term “effective temperatures” is meant all temperatures 
above 43° F, which was then regarded as a general developmental 
zero. 

Sanderson (’08) showed quite conclusively that the northward dis- 
tribution of some insect species was limited, not by the sum of effec- 
tive temperatures, but by the minimum winter temperature, and 
recommended the inclusion of this factor in Merriam’s law. 

A. D. Hopkins (718) has formulated an empirical bioclimatic law, 
stating that in general, in temperate North America, the time of 
occurrence of any given periodic event in life activity becomes later in 
the spring and earlier in the fall as we progress northward, eastward, 


ur 


PHYSICAL ECOLOGY OF THE NOCTUIDAE 


and upward. The general rate of change is four days for each degree 
of latitude, each five degrees of longitude, and each four hundred feet 
of altitude. 

The bioclimatic law does not represent conditions on the Pacific 
Coast, and there is a gradually decreasing error in its application until 
the region well east of the Rocky Mountains is reached. As the 
author of the law has stated, it is a purely empirical deduction from 
held observations, and apparently the basis of the law is the gradual 
change from marine to continental climate progressing from east to 
west as we go inland. Possibly a restatement of the law, based upon 
distance from the ocean rather than upon westward progression, 
would give smaller errors in the western part of the range. 

Aside from the general problem of the effects of climate upon 
animal distribution, efforts have been made to connect certain climatic 
conditions with specific insect outbreaks. No attempt will be made 
here to include all the work done on this problem, but a few abstracts 
will be given to show the general character of the work. 

One of the early attempts in this direction was the hypothesis 
advanced by Asa Fitch (’60) to account for army worm outbreaks. It 
is quoted in full (’60, p. 121). 

4 more briefly expressed, my view is this 
and fel swamps multiplies this insect. And when it is thus multiplied, 
a wet season and overflowed swamps drives it out from its lurking 
place in flocks, alighting here and there over the country. But on 
being thus rusticated, it finds our arable lands too dry for it and 
immediately on maturing and getting its wings again, it flies back to 
the swamps, whereby it happens that we see no more of It.” 

This view was also supported by C. V. Riley (’70, ’76), and shows 
that even in this early stage in the development of entomology, it was 
recognized that climatic factors might explain insect outbreaks. 

Charles G. Barrett (’82) gives notes on the distribution of various 
Noctuid species in an English district following two types of winter 
conditions, and concludes that the abundance or rarity of native 
species is largely determined by climatic conditions. Four successive 
mild winters made certain species, which were ordinarily common, 
very rare, and other ordinarily rare species quite common. Following 
these winters came three severe winters, after which the normal 
balance was restored. 

In considering the relation of precipitation to insect distribution, 
Criddle (’17) cited the Rocky Mountain Locust as an example of an 
insect which is increased greatly during dry seasons, and also states 
that in Manitoba the Hessian Fly is checked by a drouth sufficient to 
ripen the wheat prematurely. He shows that the combination of light 


a dry season 


6 TECHNICAL BULLETIN 12 


snowfall and low winter temperature has been fatal to the Colorado 
potato beetle in most parts of Manitoba, and considers that it will 
probably never be a major pest in that region. 

In the realm of plant ecology, especially in the study of the 
economic crop plants, there is a rapidly increasing body of work upon 
the mathematical study and analysis of climatic relations. J. Warren 
Smith (’20) brings together the principal work. relating to the effects 
of climate upon crops, using statistical methods for the more or less 
exact definition of critical growth periods. In many cases it is now 
possible to predict the amount of a given crop on a certain area if the 
weather conditions during these critical periods are known. ‘This 
work is very valuable and suggestive, and the methods used there have 
been adopted in part in this paper. 


DINEST OR SGD YSP UR SUED 

This paper is based upon studies along three distinct but related 
lines, laboratory experiments upon temperature and soil moisture 
relations, attempts to correlate these results with the conditions sur- 
rounding outbreaks of three species in the field, and a statistical 
interpretation of data relative to the effects of weather conditions on 
moth flight. The work was begun at University Farm, St. Paul, in 
1919, in connection with cutworm investigations undertaken for the 
Minnesota Agricultural Experiment Station, and carried through two 
seasons, during which time all the original data relating to Minnesota 
conditions were secured. During 1921 the work was carried on in 
Montana in connection with investigations of the life history and con- 
trol of the Pale Western cutworm (Porosagrotis orthogonia Morr.) 
for the Montana Agricultural Experiment Station, and all the original 
data relating to Montana conditions were obtained. The writer wishes 
to acknowledge his indebtedness to the authorities of both stations for 
the opportunity to study the problems, and for many courtesies 
extended during the work; and especially to Dr. R. N. Chapman, of 
the University of Minnesota, under whose direct supervision most of 
the Minnesota work was done, and whose advice and assistance have 
been invaluable. He also wishes to thank Mr. U. G. Purssell, Mr. 
C. M. Ling, and Mr. W. T. Lathrop, Meteorologists of the United 
States Weather Bureau at Minneapolis, Havre, and Helena, respec- 
tively, for their co-operation in supplying meteorological data used in 
these studies. 

METHODS, USED 

In a previous paper (Cook ’21), the author published the Minne- 
sota data relative to the effects of weather upon moth flight, using the 
method of partial correlation in their interpretation. This paper 


PHYSICAL ECOLOGY OF THE NOCTUIDAE 7 


extends this discussion, using similar methods in this part of the work 
These methods are well explained in Yule (719) and Smith (’20). The 
method of correlation depends upon the basic assumption that the 
relation between the factors studied lies along a straight line, which is 
approximately the case with the moth flight data, with the same 
exception noted in the previous paper’ (’21, p. 53). Partial correlation 
assumes a casual relationship between the factors correlated, which is 
justified in the work on moth flight, but can not be readily assumed in 
the work on the relation of climatic conditions to larval growth, so 
that in this latter case, only total correlation is used. It was found, 
upon plotting the points of the general climatic relations shown in 
Plate IV, that these did not le along a straight line, so a curve was 
fitted to them by the method of least squares (Leland ’21). Several 
other somewhat simpler but less accurate methods may be found in 
Lipka (’21), which is a valuable aid in this sort of work. 

In any study of the relation of organisms to their environment, it 
is necessary to develop some method of correlating laboratory experi- 
ments with field observations. The laboratory experiment shows what 
the organism will do in a certain controlled environment, while the 
field observation shows what it does under constantly fluctuating con- 
ditions. If we can reduce the field condition to some sort of an 
expression representing the optimum condition and can determine the 
optimum under controlled conditions, then we may say that the two 
conditions are equivalent. Because of the wide fluctuations in field 
conditions, it is necessary to treat the mean of a large series of 
observations instead of using a single observation, and the only avail- 
able method of determining field relations is that of statistics, which 
has wide social and biometric applications. The accuracy of the result 
varies as the square root of the number of observations, so that long 
series of data yield more accurate results than short series. 


COMPARATIVE CLIMATOLOGY OF MINNESOTA 
AND MONTANA 


The studies on which this paper is based were carried on under 
two essentially different climatic conditions, and these differences are 
best brought out by a comparison. It is difficult to compare two large 
areas, so the two points where moth flight experiments were conducted 
were selected as typical, and their climatic features compared. 

St. Paul, Minn., is in latitude 44° 58’ N, longitude 93° 03’ W; and 
Havre, Mont., in latitude 48° 34’ N, longitude 109° 40’ W. Both of 


these general regions are in the Transition Zone of Merriam (’98), but 


tS) TECHNICAL BULLETIN I2 


are considered as separate faunae by Thompson-Seton (’09), who 
places Minnesota chiefly in the West Alleghenian fauna and Montana 
chiefly in the Campestrian fauna. Table I, the data for which were 
secured from Henry (’06), shows the nature of the climatic dif- 
ferences between the two regions, and Figure 1, Plate I, is a climo- 
graph constructed from the data of Table I. 


= TABLE I 
CLIMATOLOGY OF HAVRE, MONT., AND ST. PAUL, MINN. 
Temperature 
Month Mean monthly Daily range’ | Humidity Total monthly 
we FP" FL 301 Sa6t- Precipitation 
Havre St. Paul Havre St. Paul Havre St) Paul Havirelest. ebaul 
Degrees Degrees Degrees Degrees Percent Percent | Inches} Inches 
January 3 12 19 18 76 76 0.8 1.0 
February 14 16 21 7, Hd 76 0.5 0.6 
March Di 29 21 18 70 68 0.6 1.6 
April 44 48 24 20 44 54 1.0 25 
May 53 60 25 20 45 51 2.1 B:3 
June 61 66 24 19 43 56 2.9 4.4 
July 68 74 | ot 35 54 2e1 3.6 
August 66 72 29 20 34 | 55 1S 3.4 
September 55 62 27 20 44 58 ileat SES) 
October 44 50 24 18 56 62 0.6 2S 
November 28 32 21 16 71 69 0.7 ily 
December 22, 20 19 16 7S) 76 0.5 132 
Meanannual 41 45 23 18 56 63 ade .- 
Total anntial |) acres ood Stes ese teers cei I ieee eee Re eee ears | eae ay el Wn ee ne 1 oy 28.6 
GENERAL CLIMATIC DATA 
Temperature Havre Sits S22 yn | Havre St. Paul 
Mean maximum, degrees.. 53 56 Average date 
Mean minimum, degrees.. 30 36 last spring frost..... May 17 May 6 
Absolute maximum,degrees| 108 104 firstetalletrosty ase elie ep Crs Octs5 
Absolute minimum,degrees| —55 —41 Average length of 
No. days above 90°...... 20 if growing season, days. 124 152 
No. days below 32°...... 168 158 ; 


The climograph is a diagram originally introduced by Ball (10) 
and modified by several workers, of whom Varney (’20) is one of the 
latest. The mean monthly figures for temperature and humidity are 
plotted against each other, and the dots for the successive months are 
connected by a line with arrowheads showing the direction of change 
in the annual cycle. A recent contribution by Flanders (’22) gives 
many variations in the use of the climograph for planting various pairs 
of weather factors. 

The summer humidity conditions are radically different in the two 
regions, the period from April to September representing in Montana 
a condition of dryness never reached in Minnesota. This dry sum- 
mer condition practically eliminates the possibility of two-brooded 
species, so that few such species occur in the plains region of 


PHYSICAL ECOLOGY OF THE NOCTUIDAE 9 


Montana. Another factor of considerable importance in the ecology 
of the moths is the large diurnal temperature range in Montana, which 
restricts flight to the late afternoon and early evening during a large 
part of the summer season. Winter conditions are very similar in the 


two regions, so that this factor should not operate to differentiate the 
two faunae. 


| LT TL abombaekrte dumborhen| | | 


PA ahevworh 
, toe pte Ss 


=] 


Fela tuve Fes rid hy 
510% | 610% 


Plate I. Comparative Climatology 
Figure 1. A comparative climograph of the annual cycles at St. Paul, 
Minn., and Havre, Mont. 


GEN PR ise GOMGG Ore int NOC LULIDARAOER 
MINNESOTA AND MONTANA 


As would be expected from the radical climatic differences, the 
Noctuid faunae of the two regions are essentially different, as 1s 
brought out in Table II, which is a compilation from Hampson 
('03-’09). The species listed as western or eastern are not confined to 
Montana and Minnesota, but represent roughly semi-arid west and 
humid east. In order to show the relations of these regions to the 
generic centers of dispersal, the number of Palearctic species in each 
genus is included. Roughly, that region showing the greatest number 
of species is generally the center of dispersal (Folsom ’06, p. 383). 

The predominating western genera are of western origin, 
apparently, and none of their species is common to Europe and Amer- 
ica, while the typical eastern genera are obviously of European origin. 
In this connection it is interesting to note the comment of John B. 


10) TECHNICAL BULLETIN 12 


Smith (90, p. 11) with regard to the character of our American 
Agrotid fauna: 

“Tt is suggestive that so large a proportion of our species are from 
the western part of our country, and that those species are mostly 
referable to those genera in which the front is modified in some way 
and the tibial armature heavy. In fact, the distinctive character of our 
western fauna is shown in the very predominance, and sometimes 
abnormal development, of tibial and clypeal armature.” 


TABLE 11 
NOCTUID DISTRIBUTION IN THE HOLARCTIC REALM 
Number of nearctic species Number of 
Eastern Western Common Palearctic Holarctic 

Genus No. America |No. America to both species species 
HUK OA Sara Sete he ae 25 163 10 84 0 
Ghorizacrotisce eee 0 5 0 4 0 
Porosacko bisa eee 1 1:2 1 0 0 
Heltia es Ase eas atk. 7 11 1 3 0 
POliae sie ee ee oe. 34 63 2 el 0 
A OT OUI Hane cee seek ee 22 17 0 79 3 
Cirphis iain we re ee ee 7 7 0 66 3 
PATASLICH LICHEN NT eee TD 9 1 16 0 
Arropenina ie ent sa ee & 3 1 1 0) 
SICdemiat ye ein each eee oe 1 2) 1 9 0 

Totals 
Western 2roupis.. 2... 4. 67 254 14 161 0 
Paster SLOuD es aan een 47 38 3 aie 6 
Grandetotalsvereey er eens 114 292 17 332 6 


The species of Euxoa, Chorizagrotis, and Porosagrotis are 
regarded by Hampson as representing the highest development of the 
Noctuid type, and this structural position is borne out by their ecology. 
They differ from the eastern species in many important respects, in 
all of which they are more highly specialized than the latter. 


LARVAL HABITS 


Cutworms may be grouped in three classes according to feeding 
habits. Climbing cutworms climb plants, eating the foliage without 
always destroying the main stem. Lycophotia margaritosa and Poro- 
sagrotis vetusta belong to this class. (Slingerland.) The great 
majority of the eastern species feed at or just above the surface of the 
ground, and may be called surface cutworms. [Examples of this type 
are Feltia ducens, Euxoa messoria, and E. tessellata. A third and 
more recent type in point of development is the group of sub-surface 
feeders, or subterranean cutworms. Among the comparatively few 
species known to have this habit, is Porosagrotis orthogoma and, pos- 
sibly, Sidemia devastator. P. orthogonia feeds entirely below the sur- 
face, cutting off plants from one to two inches below the surface of 
the soil, and moving from one to another underground, except under 


* 


PHYSICAL ECOLOGY OF THE NOCTUIDAE 11 


abnormal conditions such as heavy rainfall. All the most abundant 
Montana cutworms are either surface or subterranean feeders, with 
several species suspected of the latter habit, altho this has not been 
proved except in the case mentioned. 


ADULT HABITS 


In the habits of the adults as well as in those of the larvae, the 
species of the two regions are quite different. In the first place, the 
cutworm moths of the Montana group are very strong in flight. This 
was well shown during the early summer of 1921, when thousands of 
specimens of Chortzagrotis auxiliaris, the Western Army cutworm, 
were captured in Minnesota, Iowa, and Kansas. This species breeds 
normally in the plains region of Montana (Cooley, 716) and has never 
been reported in large numbers east of that region. This means that 
in 1921 the moths must have flown at least three hundred miles from 
the place where they emerged. 

Another peculiarity in the life history of C. ausxiliaris ee Agrotis 
unicolor Walk. (Noctua clandestina Harris), as recorded by Strick- 
land (16), is the habit of aestivation in the adult stage. The moths 
emerge in June and aestivate for a period of at least three months 
before maturation of the ovaries and oviposition. None of the com- 
mon Minnesota species (with the possible exception of A. unicolor, 
which also breeds in Minnesota) are known to have any similar habits. 
This aestivation is apparently the method chosen by these species to 
escape the intense heat and drought of July and August in Montana. 

Very little is known concerning the oviposition habits of Noctuidae, 
but all the eastern species whose habits are known lay their eggs 
directly on green vegetation. This is definitely known for Agrotis 
ypsilon, Feltia ducens, Polia lorea, Lycophotia margaritosa, and 
Cirphis unipuncta. Those Western species whose habits are known, 
on the other hand, lay their eggs either on trash on the surface of the 
soil (C. auxiliaris, Strickland ’16), or in the surface layer of the soil. 
(P. orthogonia, Parker, Strand, and Seamans, ’21). Several species 
of Euxoa are suspected of similar habits, but have not been found 
ovipositing as yet. 

In reproductive capacity the Eastern species in general outrank the 
Western, with some exceptions. Thus, it was found in Insectary work 
at University Farm that L. margaritosa lays as many as 3000 eggs, an 
average figure obtained from twenty-eight moths being 1497. Felita 
annexa (Jones, 18), lays as many as 1300 eggs, an average for ten 
females being 794. C. unipuncta has been captured with as many as 
S00 eggs in the ovaries (Turner ’18), and probably lays many more in 


12 TECHNICAL BULLETIN 12 


the field. Among the Western species, P. orthogonia averaged 315 
eggs each for five females (Parker, Strand, and Seamans, ’21), and 
C. auxiliaris laid about 1000 eggs (Strickland ’16), which figures ‘are 
the only ones available for Western species. It is evident that P. 
orthogonia, the most highly developed cutworm ecologically, does not 
need so high a reproductive capacity, as the eggs, being scattered in 
small clusters through the soil, have a much larger chance of survival. 

Another factor to be considered in connection with reproductive 
capacity is the ability of the species to produce sudden and severe out- 
breaks. A species with a high reproductive capacity can multiply very 
rapidly, and a small number of moths surviving a hard winter can 
quickly bring up the population to a destructive number. Such species 
as C. unipuncta and C. auxiliaris and L. margaritosa can produce these 
sudden severe outbreaks, as is evident from a superficial survey of the 
general economic literature. On the other hand, P. orthogonia does 
not suddenly appear in large numbers, but produces a gradually 
increasing population in any given place until checked by climatic con- 
ditions, when the cycle is recommenced. 


PHY SICA TSE CO LG GYR© FS TIVEND Es Tee Teo leno bies 


LABORATORY -SiUDiEs 

In order to obtain some experimental evidence with regard to the 
relations of the various stages of Noctuids to temperature and 
numidity, laboratory experiments were carried on at University Farm, 
St. Paul, during the winters of 1919-20 and 1920-21. It was the inten- 
iion of the writer to rear as many species as possible under controlled 
conditions, but L. margaritosa was the only species which was obtained 
in large enough numbers for this work. As atmospheric humidity has 
a very small influence on the insect during the larval stages, which are 
spent in the surface layer of the soil, the moisture of the direct 
environment, namely, soil moisture, was studied instead. 


SOIL MOISTURE RELATIONS 


The method used in determining the relations of L. margaritosa to 
soil moisture were in general those of students of plant physiology, 
being the rearing of the insect in a cage of soil whose known moisture 
content was held approximately constant by the daily addition of suf- 
ficient water to maintain a constant weight. Lantern globes covered 
over the top with coarse muslin were placed over the soil in a pot hold- 
ing about five pounds of soil. The original moisture content of the 
soil was determined, sufficient water added to secure the required 
moisture content, the weight of pot, soil, and cage taken and held 


PHYSICAL ECOLOGY OF THE NOCTUIDAE 13 
constant throughout the experiment. The freshly-laid eggs were 
placed on the surface of the soil in the cage, and the insects reared to 
the adult stage under the same constant moisture condition. A 
thermograph was kept in close proximity to the cages to give a con- 
tinuous record of air temperature, and all cages were kept close 
together in the greenhouse under as uniform conditions as possible. 
Two sets of experiments were performed, differing slightly in details, 
and will be considered separately. 

First experiment—1919-20.—In this experiment three soils were 
used, a course sand with a maximum water capacity of about 32 
per cent of dry weight; a rich leaf mold with a water capacity of 
about 52 per cent of dry weight; and a mixture of equal parts of these 
two, designated as loam, whose water capacity was about 41 per cent 
of dry weight. Two cages were held at each moisture condition, of 
which there were sixteen. The cages were examined each morning, 
and the number and instar of the larvae present noted, so that the 
figures given represent an average for the larvae of each two cages. 


(LABibhe Lhe 
MOISTURE RELATIONS OF LYCOPHOTIA MARGARITOSA 
First EXPERIMENT, 1919-20 
Water Content 
per cent of No. off Egg |No. of} Larval | No. of Pupal No. of | Total Mor- 
___————=*sS|:séeeggs:«=| period | larvae} period pupae period adults life tality 
Dry Total 
weight capacity 
days days days days|Per cent 
SAND} SERIES 
5.0 eS 50 6.0 30 53.0* 0 Rees 0 59.0* 100.0 
(es 23 17 8.0 14 36.5* 1* Sys 0 44.5% 100.0 
10.0 32 24 7.0 13 9 Ie Ks 10) ay 0 29.3* 100.0 
P25 39 18 8.0 12 59.6 2, DM A 2 89.5 96.4 
15.0 47 60 7.0 52 58.1 7 22.3 3 92.3 95.0 
20.0 63 ak 9.0 20 Spas 4 32.0 1 91.0 96.3 
Series 196 TES 141 56.9 14 25.6 6 91.2 96.9 
LOAM SERIES 
5 14 30 7.0 2 8.0* 0 ee 0 TMS Obs 100.0 
10 28 30 7.0 14 a fe 0 ane 0 54.1* 100.0 
ily 42 30 6.0 23 5 SiG 4 23-2 4 $1.2 86.7 
20 56 34 7.0 19 51.9 9 23.0 8 85.1 76.2 
25 70 28 9.0 14 53.8 4 32.0 2 89.0 92.9 
35 98 36 9.0 6 Sar 2 22.0 1 82.0 88.9 
Series 191 PS 78 5202 19 24.3 LS 84.4 92.1 
LEAFMOLD SERIES 
10 19 pH | 7.0 20 56.5 17 bet 0) 63.5 100.0 
20 38 28 8.0 22 50.6 1 2520) 1 92.0 88.9 
30 Oy, 26 8.0 j WP 33.0 + 0 Tear: 0 39.0+! 100.0 
40 | 76 Lan 8.0 10 48.0 4 23.6 3 80.0 82.4 | 
Series | 98 1.7 54 48 3 6 23.9 4 83 0 << 95.9 


*insects apparently died from lack of moisture before emerging as adults. 
+Larvae in this cage killed by a fungous disease. 


Considering both duration of stages and mortality, the loam was 
the most favorable soil for growth. The minimum water requirement 
of the species seems to be about 35 per cent of the total capacity on 


each soil, and the optimum is above 50 per cent. There seems to be 


14 TECHNICAL BULLETIN a2 


no upper limit, altho probably a very wet soil is more favorable to the 
development of fungi in the field, thus reducing the numbers of 
insects. 

Second experiment—1920-21.—The second set of experiments 
was run as a check on the first, and was conducted in the same 
greenhouse, under the same general conditions. Only one soil, a loam 
mixture with a water capacity of 32 per cent, was used, and five cages 
were run at each of six moisture conditions. In addition to the 
thermograph as in the first experiment, readings were taken each 
morning of the temperature of the surface soil in each cage, from 
which the departure of that temperature from that of the thermograph 
was computed and the actual temperature condition in the cage deter- 
mined. Records were kept only of dates of hatching of eggs and 
emergence of adults, together with the number of adults emerging, 
from which the mortality percentage is calculated. The results of this 
experiment are given in Table IV. 


TABLE IV 


MOISTURE RELATIONS OF LYCOPHOTIA MARGARITOSA 
SECOND EXPERIMENT, 1920-21 


Water content Larval 
Per cent of and 
pupal 
Dry Total No. of Egg period No. of Total Mor- 
weight capacity eggs period adults life tality 
days days days Per cent 
5 15 128 7 59.4 15 66.4 88.3 
10 31 108 TD 68.5 13 76.0 87.9 
BS) 47 80 Ths oe 11 82.6 86.2 
20 62 99 8.5 76.6 25 85.1 74.8 
25 78 85 9.0 83.6 12 92.6 85.9 
30 94 90 9.0 78.6 21 87.6 76.7 


The minimum moisture requirement is not so evident in this 
experiment as in the first, but there is a definite optimum moisture of 
about sixty per cent of capacity. In order to show the general trend 
of both experiments, the data of Table III are combined with those of 
Table IV to form Table V, in which the various moisture contents are 
erouped into four general classes. 


TABLE V 
MOISTURE RELATIONS OF LYCOPHOTIA MARGARITOSA 


Water 
per cent cf No. of No. of Total Mortality 
total capacity eggs adults life 
Days Per cent 
OktouesS 314 28 71.0 93.2 
SO6\toO) 50 222 21 84.8 90.5 
S1stoOr OS 183 34 85.3 81.4 


66 to 100 256 39 88.5 84.8 


PHYSICAL ECOLOGY OF THE NOCTUIDAE 15 


The general conclusion to be drawn from these experiments is that 
the Variegated cutworm has a definite moisture requirement, both 
optimum and limiting, and that the optimum condition is about sixty 
per cent of the total water capacity of the soil. 


TEMPERATURE RELATIONS 


Experiments were planned for the rearing of all stages of 
L. margaritosa under controlled conditions of temperature, but it was 
found that any obtainable constant temperature was too high for the 
larval and later stages. The mortality was 100 per cent at all temper- 
atures above 23° C., and only a single adult was secured at this 
temperature. Experiments on the hatching of the eggs were more 
successful. Table VI shows the results obtained from the exposure of 
twenty-four masses of 50 to 400 eggs each to three different constant 
temperatures. Four of the masses exposed to 30° C. failed to hatch, 
and only a portion of the eggs in the other six masses hatched, show- 
ing that this temperature approaches the upper limit of growth. The 
figures for duration of egg period are weighted according to the num- 
ber of individual eggs in the experiment. The figures in the columns 
headed “Index of development” and “Thermal constant” are derived 
as explained in the introduction in the discussion of the work of 
Sanderson and Peairs (’13). 


TABLE VI 
TEMPERATURE RELATIONS OF LYCOPHOTIA MARGARITOSA 
EGG STAGE 
Temperature (C) Duration 
1/(6) (2) x (6) 
No. of Index of Thermal 
Observed Effective masses Max. Min. Mean development constant 
(1) (2) (3) (4) (S) (6) (7) (8) 
Degrees Degrees Days Days Days 
23 14.2 10 55 5.0 ae .192 73.84 
27 18.2 4 4.0 4.0 4.0 .250 72.80 
30 yale. 10 4.5 4.0 4.1 .244 86.92 


In the second series of moisture experiments, daily readings were 
taken of the temperature of the surface soil of each cage, from which 
the actual cage temperature was computed. In Table VII are given 
these temperature figures for the egg stage, together with the data on 
duration of the egg period and computations of the index of develop- 
ment and thermal constant on the basis of effective temperatures, as 
in Table VI. 

The results of both these experiments are plotted on Plate II, the 
points for the two series being distinguished by the use of two 
symbols. The agreement of the two sets is more than accidentally 


16 TECANICGAT BE Leer ene 


close, and we must conclude that moisture in itself has little influence 
on the egg stage, except as it acts indirectly, by reducing temperature. 
Figure 1, Plate II, shows the temperature hyperbola: drawn through all 
the points, and Figure 2 shows the reciprocal line. 


TABLE VII 


TEMPERATURE RELATIONS OF THE EGG STAGE OF LYCOPHOTIA MARGARITOSA 
UNDER CONTROLLED MOISTURE CONDITIONS 


Water f Temperature (C) 
per cent of 
total No. of Egg Mean, Mean, Index of Thermal 
capacity eggs period air cage development constant 
Degrees Degrees 
15 189 7.0 20 19.88 143 77.56 
31 157 tas 20 18.99 AUST) 76.43 
47 163 ths 20 18.26 .133 70.95 
62 156 8.5 20 1 fe OS 118 70.98 
78 85 9.0 20 16.44 ake 68.76 
94 90 9.0 20 16.52 “fila 69.48 


PIE UL DSANDES PATI S IGA es LUD 

Very early in the course of these studies, in considering the rela- 
tions of L. margaritosa to temperature and soil moisture, it became 
quite evident that a knowledge of these optimum and limiting condi- 
tions should be of great value in a study of the relations of meteoro- 
logical factors to insect outbreaks. For example, knowing definitely 
that the optimum soil moisture condition for this species is about 60 
per cent of the total moisture capacity of any soil, would it not be a 
logical step to assume that field conditions during a destructive out- 
break must at least approach this condition? If this assumption is 
correct, and the writer believes it to be, then, working back from this 
hypothesis, the weather data, in terms of temperature and precipita- 
tion, for the infested region during the period of the outbreak, must 
represent this optimum. This, then, is the first problem. Is there any 
definite indication of an approximately constant moisture condition in 
the field, as expressed in the temperature and precipitation records, 
and, if so, in which parts of the life history of the insect is this relation 
most pronounced? Further, if possible, it is desirable to analyze the 
weather data for the period covered by the destructive generation of 
the insect and by the preceding winter generation, that is, for a period 
extending at least a year previous to the outbreak, comparing condi- 
tions in all months, in order to obtain indications of any relationships 
which might aid in the climatological interpretation of the outbreak. 

As it is necessary to deal with a large body of data in order to 
obtain trustworthy results, it is evident that some method of analysis, 
preferably some well-known standard method, must be used. For this 
work the method of correlation, as developed by the writers referred 
to in the introduction, is well adapted. The meteorological relations of 


PHYSICAL ECOLOGY OF THE NOCTUIDAE 17 


C. unipuncta in Minnesota have been quite carefully analyzed by this 
method, and some of the more general relations of L. margaritosa and 
P. orthogonia, altho the work done on these last two species is of a 
preliminary nature, introduced in this paper for purposes of com- 
parison. 


N 
ies PHOTIA| MARGARITOSA 
po || eas = 


LYCOPHOTIR TOSA 4 
4 S) ariable TemptraTure, 
Constant Mo:sfure 
Jdo000 10 ahs f i oe : 


Plate IJ. Temperature Relations 


are 
Pere 
a 


° 
y Y tb q i 
® 


a 


hy q 
st 
q 


aH 
D 
> 

5 b 


) 
K> 


Figure 2. Hyperbolic temperature-growth curve for the egg stage of 
Lycophotia margaritosa, 

Figure 3. Reciprocal growth curve for the egg stage of Lycophotia mar- 
garttosa, 


18 TECHNICAL BULLETIN 12 


METEOROLOGICAL RELATIONS OF CIRPHIS UNIPUNCTA 


Since 1895 there have been five major outbreaks of the army worm 
in Minnesota, which form the basis of this study. The general method 
of attack consisted in determining first the distribution of the insect in 
each outbreak, plotting the area roughly on a map, selecting all the 
United States Weather Bureau stations inside this area, and assembling 
the weather data for each station for the entire year preceding the 
outbreak. Out of about seventy-five station records so secured, 
twenty-one points were selected which had been in the area of destruc- 
tive abundance for at least two of the five outbreaks, and their records 
were assembled for the entire period, 1895-1920. As some of the 
records were not complete for the entire year preceding an outbreak, 
those incomplete records were eliminated, leaving a series of thirty-five 
records, which were finally used as the basis of the statistical study. 
This elimination secured a set of records from a single region, each 
one represented more than once in the series, and all of them in 
regions more than normally liable to army worm attacks. A description 
of the area covered by each outbreak, the sources of information con- 
cerning each, and a list of the stations used for each in the statistical 
work follows. 

1. 1896. <A very widespread and destructive outbreak occurred 
throughout the southern and southeastern parts of the state. Data in 
regard to distribution were obtained chiefly from files of the daily 
newspapers of the region for the period, on file in the Library of the 
Minnesota Historical Society. The stations used were Farmington, 
Luverne, Montevideo, and Winona. 

2. 1906. A more local outbreak occurred in the southwestern 
part of the state, extending some distance north of the Minnesota 
River into the southern portion of the Red River Valley. The dis- 
tribution of the insect in this and succeeding outbreaks was obtained 
from records and correspondence filed in the office of the State 
Entomologist. The stations selected were Alexandria, Bird Island, 
Fergus Falls, and Morris. 

3. 1910. A widespread outbreak occurred over the same territory 
covered in 1896, but with the most severe damage in the southwestern 
part of the state. The selected stations were Alexandria, Bird Island, 
Fairmont, Fergus Falls, Montevideo, Morris, New Ulm, Redwood 
Falls, and Windom. 

4. 1919. A very widespread and severe outbreak of the army 
worm, accompanied almost universally by L. margaritosa, covered the 
entire southern part of the state and extended up the Red River Valley 
as far as Crookston. This outbreak and the one in 1920 were per- 


a> 


PHYSICAL ECOLOGY OF THE NOCTUIDAE 19 


sonally investigated by the writer. Selected stations were Albert Lea, 
Bird Island, Fairmont, Farmington, Grand Meadow, Luverne, Lynd, 
Montevideo, New Ulm, Redwood Falls, St. Peter, Winona, Worthing- 
ton, and Zumbrota. 

5. 1920. A locally severe outbreak occurred over an area embrac- 
ing portions of the counties of Rock, Pipestone, Murray, Cottonwood, 
Lyon, and Redwood. The stations chosen were Bird Island, Luverne, 
Lynd, and Montevideo. 

Complete data for these stations may be found in the files of the 
“Climatological Data, Minnesota Section,’ of the United States 
Weather Bureau. 

Having assembled these data, the next step is the search for some 
methods of interpretation which will bring out the presence of a given 
moisture condition such as was outlined above. A consideration of 
the relationship between temperature, precipitation, and soil moisture 
makes it evident that, considering the variation in the evaporating 
power of the air at different temperatures, a heavy precipitation at a 
high temperature would produce the same moisture condition in the 
soil as a lighter rainfall at a lower temperature. That is, for example, 
the moisture at 70 degrees F. and four inches precipitation would 
probably be equivalent to that at 60 degrees F. and three inches rain- 
fall. In other words, if we plot the temperature and precipitation 
figures for the thirty-five stations on a dot chart, whose ordinate is 
temperature and whose abcissa is precipitation, placing a dot at the 
intersection of the axes representing the condition at each station, a 
positive correlation between temperature and precipitation would rep- 
resent the presence of an approximately constant moisture condition 
at all the stations. The closer the relationship, and the nearer the dots 
approach a straight line, the higher the value of the coefficient of cor- 
relation, ‘‘r,” and the more critical this relationship in the economy of 
the species. 

A series of dot charts, constructed as outlined above, were prepared 
for the conditions in each month of the year preceding an army worm 
outbreak, each chart containing the thirty-five points representing the 
selected stations. The correlation coefficient, “r” was calculated for 
each chart, together with its “probable error.” The significance of ‘“‘r”’ 
is related to its probable error, a value less than three times the prob- 
able error being of little significance, and one of more than six times 
the probable error indicating a very critical relationship. In order to 
determine whether these correlations were entirely due to the condi- 
tions in years preceding army worm outbreaks, a second series of 
charts was constructed, one for each month, on which the temperature 


20 TECHNICAL BULLETIN 12 


and precipitation for the twenty-one stations for the entire period of 
twenty-five years were plotted. The difference between the correla- 
tions in the latter set and those in the former set indicated the true 
relationship of these conditions to army worm outbreaks. Both sets 
of coefficients and probable errors are given in Table VIII. Those 
months in which the value of “r’’ was near to six times its probable 
error, and in which it varies greatly in the months preceding army 
worm outbreaks from the value for the same month in the whole 
period, are regarded as critical, and the month and value are repeated 
in the fourth column. 
TABLE VIII 


CORRELATIONS OF TEMPERATURE WITH PRECIPITATION 


35 Selected stations Significant 
21 Stations for period correlation 
Month entire period preceding or 
1895-1920 army worm critical 
outbreak period 
ATP US tae eee ae +.129 +.031 —.007 +.113 
SEDtEMDEeH aes eee +.038 +.033 +.421 +.093 +.421 September 
Octobencne: seers — .064+.033 +.571+.077 +.571 October 
INOVeMm Deiaceeee ae +.029 + .033 +.481 +.088 +.481 November 
Decemberns ware +.017 +.033 Ss eee Se 2 
anita tyep eee eet —.251 +.031 —.227 +.108 
Hebatianyvaceacee oe +.319 +.030 +.242 +.107 
Marcha arate —.390 +.028 —.416 +.094 
Aprites tacts caceuct +-.012 =.033 —.318 +.102 
Ma). cae Not ese +.096 + .033 +.548 +.079 +.548 May 
Jina hater —.005 +.033 +.122 +.110 
July Ss eet eee —.169 +.032 +.159 +.110 


Analyzing the data in this manner shows that without any reason- 
able doubt, there is present some definite, practically constant moisture 
condition during the period preceding the outbreak, and that this cond1- 
tion is most marked in the months of September, October, November, 
and May, or during the larval life of the overwintering generation. 
The correlations in the winter months are fairly high, but correspond 
closely to those for the twenty-five year series, and hence are not 
necessarily related to army worm outbreaks. 

The next logical step would be to ascertain whether this moisture 
condition is approximately equivalent in the various critical months, 
but we will postpone this consideration until some other relationships 
are studied. Let us next study the relations between successive 
months, for the purpose of determining the presence of any seasonal 
succession which is of importance. A consideration of the problem 
will show that a negative correlation between temperature in two suc- 
cessive months shows the presence of a necessary constant temperature 
sum for those two months. That is, if a warm September is followed 
always by a cold October, and a cold September by a warm October, 
the sum of temperature for the two months will tend to remain con- 
stant, and it remains for us to determine the significance of this 
thermal constant in the economy of the army worm, 


PHYSICAL ECOLOGY OF THE NOCTUIDAE 21 


In order to test the presence of any such relationships, dot charts 
and correlations were made by combining the temperature of each 
month with that following, and with various other months where there 
seemed to be any indication of a critical relationship. The same 
procedure was followed with the precipitation data, and the more 
significant of these correlations are given in Tables IX and X. 


TABLE IX 
TEMPERATURE RELATIONS BETWEEN SUCCESSIVE MONTHS 
PRECEDING ARMY WORM OUTBREAKS 


ers YT 


September October November December January June July 
September —.924 —.723 —.665 —.745 —.619 —.718 
October +.796 +.781 +.884 +.785 +.770 
November +.557 +.760 +.571 
December +.928 +.378 
January +.567 
June +.788 
July 
TABLE X 
PRECIPITATION RELATIONS BETWEEN SUCCESSIVE MONTHS 
PRECEDING ARMY WORM OUTBREAKS 
September October November December January June July 
September —.364 —.170 —.254 —.361 
October +.429 + .323 +.556 
November 
December 
January 
June +.607 
July 


Altho no general correlations were made, as in the case of the first 
set of computations, it seems probable that these correlations given 
here are all significant, especially those between successive months. 
Vhe most interesting relationships are found in the temperature cond1- 
tions in the fall and early winter months. Considering first, September, 
October, and November, as they are the months in which the young 
larva prepares for hibernation, it is apparent that there is a very high 
correlaticn indicating the existence of a constant sum of temperature 
for those three months. If September is warm, October and Novem- 
ber are cold, and if September is cold, October and November are 
warm. In order to test for the presence of this thermal constant, the 
mean temperature for October and November was computed and cor- 
related with the September temperature, which gave a value of —.77] 
for “r.” Then the mean temperature for the three months was com- 
puted for each station, and found to be 46.92, ranging from 43.6 to 
49.7 F., with a standard deviation of 1.44 degrees. The standard 
deyiations of the monthly temperatures of which this sum was com- 
posed were 3.70, 3.47, and 3.56 degrees, respectively. 


22 TECHNIGAL“BULEET INI 


The significance of this thermal constant in the economy of the 
insect evidently is in enabling the insect to reach a certain stage in 
which it is best able to hibernate. Knight (’16) has shown that this 
species can not hibernate in New York in the pupal stage, and evidently 
the range in Minnesota is even narrower, probably being restricted to 
two or three certain larval instars. 

Another interesting temperature relationship is that between Sep- 
tember and December and January, considered together. The relation- 
ship is even higher when October is substituted for September. This 
shows a very interesting balance between fall and winter conditions. 
If September is warm, the young larva grows quite rapidly, but its 
growth is checked by the cold weather in October and November, and 
this gradual “hardening” process enables it to withstand low tempera- 
tures in the early winter. On the other hand, if September is cold, 
the slow growth is accelerated during the warm October and November 
which follow, and the larva does not have the gradual hardening period 
found in the former case, and is evidently unable to withstand such 
cold weather in the early winter. These relationships are evidently 
vital to the insect, and a more complete analysis of these and others 
of lesser importance would probably enable us to predict the occur- 
rence of army worms in any given locality by a study of the weather 
data for the previous year. 

On Plate III are shown a few of these dot charts for the correla- 
tions in the fall and early winter months. The relationships are very 
close for this class of data, and their importance should not be under- 
estimated. Notice particularly the high correlations between tempera- 
tures of successive periods, which are almost perfect in one case and 
of high value in the others. 

Now, returning to the consideration of the question raised earlier 
in the paper as to the equivalence of the moisture conditions in the 
various months, we will study that point more intensively. First, it 
will be of value in visualizing the situation to show graphically how 
the condition in each of these months departs from the average of the 
region for twenty-five years. This is shown in Figure 4, Plate III. 
The heavy central axes represent the normal condition, and departures 
are measured from these in degrees F. and inches of rainfall. A circle 
represents the position of each month with regard to normal condi- 
tions. Six of the months are in the “warm, wet” quadrant, three in 
the “warm, dry” quadrant, and three in the “cool, dry” quadrant. 
None of them are in the “cool, wet” quadrant, a condition probably 
favorable to fungous parasites. The winter months are all warm and 
none of them very wet, indicating that a warm winter, with light snow- 


PHYSICAL ECOLOGY OF THE NOCTUIDAE 23 


fall, and presumably frequent freezing and thawing periods, is favor- 
able to this species. This is also the case with the Pale Western 
cutworm, to be noted later. 


Ee 


62-1150 -/100" - 0 {50° 
(Wart, Dav) 


° 


Tempera ture| yn in Sthemb r on 


cab ee ee ice ed ea 


fean Te Real nae -jan — 
ae 2 
e . 
re ene 


peray 
Ttkbera 
AA pera lu 

Cie aioe ty Dacembertand Japuary 

CPT PET Aare s: Pr mig! trim orm ° 
ODE aL “~ pias LA \ 
‘neceding Army Worm 
Outbreaks be es 
1 J55° p Ae ached 


Ary Whe Osprey 
Pale es ao 


Figak 8 
etiSeplember Telmpera 


A 
fe 
aTure > 


S a 
ae 


S : 
J 
AN 
Sa 
3 
2 
x3 
S 
J 


Plate III. Meteorological Relations of Cirphis unipuncta 


Figure 4. Departures of monthly mean conditions from their respective 
normals during the period preceding outbreaks of Cirphis unipuncta. 


Figures 5, 6, 7, 8, 9. Correlations between the weather factors in the period 
preceding army worm outbreaks. 


5. September temperature and precipitation 
October temperature and precipitation 
September temperature and October temperature 


September temperature and mean October-November temperature 


Oo OND 


October temperature and mean December-January temperature 


24 TECHNIGCAL*BULIEETIN 12 


== = 


Argure elo be Army Worm Figure Lt The Vahega tea Caran 
A/s\unt c/a Hd» | Lycophotia |margarfesa faw. 


us | 
‘ | 
| 
— Fred — Mecipi tation (vy) 1 
#2 4: A p— bia ¢ 


ARS FW 


Plate IV. net alone Relations of Rreeeidee 

Figure 10. Moisture curve of Cirphis unipuncta 

Figure 11. Moisture curve of Lycophotia margaritosa 

Figure 12. Moisture curve of Porosagrotis orthogonia 

Figure 13. The three curves combined, to show comparative conditions 
and general distribution. 

In the early part of this study, it was brought out that a positive 
correlation between temperature and precipitation in any one month 
indicated the existence of a nearly constant moisture condition. This 
line would be approximately straight in considering the range of tem- 
perature in any one month, but would probably be a curve when the 
wide range of annual conditions is considered. As the amount of 


* 


_ 


eo 


PHYSICAL ECOLOGY OF TAE NOCTUIDAE 25 


moisture in the soil is a function of the evaporation of the air as well 
as of temperature and precipitation, this curve should be of the same 
general type as the curve which shows the amount of water vapor the 
air can evaporate at any given temperature, in other words, the vapor 
pressure curve of water. The formula for this, as given by physical 
chemists, is approximately 
log P, La5W Cie 15) 
2.3025 — = 
log P, 1.99 lad 

We are not primarily interested in the various constants of this 
curve, P representing vapor pressure; T, temperature, and W the 
latent heat of vaporization, but we will note that it is logarithmic in 
nature, and hence, if the temperature and precipitation points for the 
various months are plotted on a graph, they should be capable of rep- 
resentation by a similar logarithmic curve. Such a graph is shown in 
Figure 10, Plate IV, and a curve computed to fit the points, whose 
formula is given in the figure. The writer wishes to emphasize the 
point that the selection of that particular formula was the result of 
more or less guesswork, altho the constants are computed by least 
square methods, and are accurate for that type of curve. It is possible 
that future work will show that some other form of exponential curve 
will express the moisture relations of the army worm more accurately. 
However, the curve is semi-logarithmic, and a plot of the points on 
semi-log paper shows them to fall in the neighborhood of a straight 
line, which justifies the assumption of that type of formula. 

To summarize the results of the analysis of the meteorological rela- 
tions of Cirphis unipuncta, we may state the following conclusions : 

1. The army worm evidently has a definite optimum moisture 
requirement, as shown by the various correlations, which can be 
expressed in terms of temperature and precipitation by the logarithmic 
formula 


log Y = 9.85188 — 10 +- .00999 X 

in which X represents temperature and Y precipitation. Substitution 
of given values of X in the equation give the corresponding log Y, 
from which Y may be found. This equation represents the general 
optimum condition, and any place whose annual conditions approach 
this curve lies within the normal range of the species, and is liable to 
infestation whenever the particular requirements outlined below are 
satisfied. 

2. In Minnesota, where hibernation takes place in the larval stage, 
the sum of temperatures during September, October, and November 
must approach 3 x 46.92° F. 


26 THECANICAL  BULLEEIN IZ 


In addition, the temperature for the two months of December and 
January taken together must bear the relation to that of October 
expressed by the equation 

Dec. temp. + Jan. temp. = 3.35 Oct. temp. — 120.4° 

which equation is derived from the correlation in Figure 9, Plate IIT. 
The above are the most important particular requirements which must 
be fulfilled in Minnesota before an army worm outbreak occurs. 
There are probably other minor conditions which combine with these, 
but which are not so vital. The relation between temperature and 
precipitation must, at least in September, October, November, and 
May, approach the general condition outlined above. 


METEOROLOGICAL RELATIONS OF LYCOPHOTIA MARGARITOSA 


Unfortunately for this study, the only outbreak of this species in 
Minnesota concerning which we have definite information available 
was in 1919, in association with C. unipuncta, as was mentioned above. 
With only this single outbreak as a basis, it seemed futile to attempt 
much statistical work, as the results obtained would be of but slight 
value. However, a comparative study of the weather data for this 
outbreak and that for the other four army worm outbreaks should 
yield some evidence as to the points of difference which made possible 
the extreme abundance of L. margaritosa. Accordingly, the stations 
listed for 1919 were separated from the rest of the data, and their 
means computed. These figures, together with those for the Pale 
Western cutworm, will be found in Table XI. 

These means were then plotted in a manner similar to that used 
with the mean figures for the army worm outbreaks, and a similar 
exponential curve plotted to fit them, whose equation is 

Log ‘Y == 0.03695: + .00845'X (Plate 1V,*Fig. 11) 

This curve differs chiefly from the army worm curve in the size of 
the constant term, indicating a larger basic amount of rainfall, and 
showing that the Variegated cutworm prefers conditions more moist 
than the army worm. 

Knowing from laboratory experiments that the optimum moisture 
condition for this species is about 60 per cent of total water capacity, 
we can conclude that this curve represents an approximation to this 
condition, and hence that the army worm curve, which represents a 
slightly lesser amount of precipitation for any given temperature, 
indicates the optimum for that species to be slightly lower, probably 
in the neighborhood of 45 to 50 per cent of total capacity. The writer 
has been unable as vet to confirm this fact experimentally, and it would 
be a matter of considerable interest and value to do so. 


PHYSICAL ECOLOGY OF THE NOCTUIDAE 27 


Because the data are so meager, it is impossible to draw any con- 
clusions with regard to any necessary succession of seasonal conditions, 
as was done in the case of the army worm, so this part of the study is 
incomplete. 


METEOROLOGICAL RELATIONS OF POROSAGROTIS ORTHOGONIA 


The two species whose climatic relations we have been considering - 
are both normal inhabitants of the humid region of Minnesota, and 
their moisture requirements are those natural to species of this region. 
We will now consider these relations of Porosagrotis orthogonia, a 
species whose habitat is a region with a normal rainfall of about four- 
teen inches per annum, as compared to twenty-eight in Minnesota. It 
is apparent that the moisture requirement of such a species must be 
very much lower than those of the former two species, but it is not at 
once apparent just how much lower it should be. 

The Pale Western cutworm is a species which has very recently 
become of great importance in many parts of Montana. It was first 
noted in large numbers in 1915, and has since been rapidly increasing. 
For a sketch of its distributional history, the reader is referred to 
Parker, Strand, and Seamans (’21). The chief point of interest in 
connection with its rapid increase is the fact that the last five years 
(1917-21) have been a period of almost unprecedented drouth over 
the infested regions, which has evidently been an important factor in 
the ecology of the species. From distributional data on file at the 
Entomology Department, Montana State College, maps were con- 
structed as in the case of the army worm, and United States Weather 
Bureau stations were selected as representative of conditions in the 
infested regions. As this study is still in the early stages, the distribu- 
tion and list of stations will not be published. | 

Two points noted at the beginning of the study are of interest, 
and will be mentioned. Tirst, a very superficial study of these distri- 
butional maps in connection with maps showing the annual distribution 
of precipitation for the period made it very evident that the greatest 
amount of damage in any year fell within the area of the state receiv- 
ing less than twelve inches of rainfall. This shows beyond a doubt 
the semi-arid character of the optimum condition. Second, a plotting 
of the monthly means for a period of about a year preceding outbreaks, 
obtained in each case by the averaging of about forty points, gave the 
distribution curve shown in Figure 12, Plate [V. Computing the 
constants for this curve by the method of least squares gave the equa- 
tion for this species as 


Log Y = 9.48837 — 10 + .01158 X 


28 TECHNICAL BULLETIN 12 


Thus this curve, of a similar formula to the other two, varies in the 
size of the constant term, and also in the greater value of the X term, 
indicating a greater curvature than in the other cases. An inspection 
of this curve as plotted shows the much smaller amounts of rainfali 
necessary to produce the optimum for this species. 

Another relation, on which very little work has been done other 
than a preliminary examination of the data, is the relation to winter 
conditions. Such an examination showed that winter conditions in 
years and places preceding outbreaks were warmer than normal, and 
drier than normal. Thus, this species, like the army worm, can with- 
stand a considerable amount of freezing and thawing better than 
steady cold weather with a heavy snow blanket. 


COMPARATIVE CLIMATOLOGY 


Now that the general climatic relations of these three species have 
been outlined, it is of interest to compare these conditions with each 
other and with other places, to show the significance of these relations 
in the consideration of general distribution. Table XI gives the com- 
parative conditions in the months preceding outbreaks of the three 
species studied. 

TABLE XI 


COMPARATIVE CLIMATOLOGY 


Month Porosagrotis Cir phis Lycophotia 
preceding orthogonia unipuncta mar garitosa 
Outbrea < p> 4 

Temp. Precip. Temp. Precip. Temp. Precip. 

Degrees Inches Degrees Inch s Degrees Inches 

AS Shee ne eae 66.5 jn en Rae er tare Mies ie eee pe CRI uP Pac Beee Mee! so ABO) Ole ere 
September....... Oat faa 59.4 Des) ya) 1.6 
Octoberst aaa 41.4 es 47.0 1.8 51.0 SD, 
INoOvem bGines see 28.6 0.6 34.1 2.6 36.9 re, 
December 18.7 0.6 20.1 ial pli hay p 1.6 
ania tyre oil sal 0.5 17.6 0.7 ZS22 0.5 
Rebriaty. 4 ese Del 0.5 15.8 ee es Das 
Nacht seen DERG 0.5 33.0) Absit 31.7 iba? 
PNG OVRUNS ee a 41.4 ee 46.8 Sia: 45.4 3.8 
INTaNy ieee eel rome Lyrey CA 56.6 2.6 56.9 2.0 
Junction ae 59.4 2.0 68.3 Sys) 69.6 6.9 
Julyee sss Soak Aa ee te oe eee ree TAS on 74.3 4.6 
Totaliprecipitation!| esse ere TOs Sige i pee es vhtes cer 25 Age Vl ea eer at 30.2 


This table shows conclusively the wide variation in the moisture 


requirements of the three species, a fact which is shown graphically - 


in Figure 13, Plate IV, on which all three of the curves are drawn in 
their relations to each other. 

lf these lines really represent the moisture requirements of these 
species, any location in which one of them is normally found should 
approach the moisture conditions indicated by the particular line. In 
order to test this out, three points were chosen, one of which is within 
range of the Pale Western cutworm, one in the range of the army 


%, 


ta 


PHYSICAL ECOLOGY OF THE NOCTUIDAE 29 


worm, and presumably, of the Variegated cutworm, and one of which 
is outside of the range of the army worm, but possibly, under excep- 
tional conditions in the range of the Variegated cutworm. ‘The three 
points chosen were Glasgow, Mont.; Ithaca, N. Y.; and Jacksonville, 
Fla. The data for their mean monthly temperatures and precipita- 
tions were obtained from Henry (’06), and plotted on Figure 13 in 
their proper relation to the three curves. The lines drawn connecting 
the outside points of each station are of no especial significance, but 
are merely introduced to bring out the general conditions at each point 
more clearly. In the cases of Glasgow and Ithaca, the points are in 
very close relation to the respective cutworm curves, showing that they 
normally approach the necessary moisture condition. The condition at 
Ithaca is of special interest when considered in connection with the 
theory of Fitch (°60) which was evolved from a study of New York 
conditions. Ithaca is normally slightly to the “wet” side of the army 
worm curve, which accounts for the occurrence of army worms there 
following dry seasons, as Fitch has indicated. 

Jacksonville is not only at a considerable distance from either of 
the curves for army worm and Variegated cutworm, but the major 
axis of the polygon lies at a considerable angle to these curves. Tlius 
it would not only take a wide variation in conditions to bring about an 
army worm outbreak there, but this variation would have to be such 
as would twist the axis of the distribution through a considerable 
angle, a condition which practically excludes the possibility of exten- 
sive outbreaks in that region. 

It is hardly conceivable that either of the last two places would 
ever become dry enough to be infested by the Pale Western cutworm, 
or that Glasgow would ever be wet enough to be infested by the 
army worm. 

CONCLUSIONS 

We may summarize the results of the studies on the relations of 
meteorological conditions to outbreaks of these three Noctuid species 
in the following statements. 

1. Each of these species has a definite optimum and lin«ting soil 
moisture requirement, which has been ascertained directly by labora- 
tory experiments in the case of Lycophotia margari.osa, and indirectly, 
by a study of conditions surrounding outbreaks in the case of the 
other two species. This moisture requirement is capable of mathe- 
matical expression in the form of an equation similar to that express- 
ing the relation of vapor pressure of water to temperature, giving 
directly the optimum condition in terms of temperature and precipita- 
tion during the growth period of the species. These three equations 
fitted to the data for the three species are: 


SO TECHNICAL BULLETIN 12 


A. Pale Western cutworm....Log Y = 9.48837 — 10 + .01158 X 
B., Amy wore ec. 1c eer Log Y == 9.85188 — 10 + .00999 X 
Cr aVariepated citwornt = a Log Y = 0.03695 + 00845 X 
jx 


These soil moisture curves may be used to indicate the distri- 
bution of each species by plotting the mean data for any station on 
the same graph and comparing their location with the curve. 

3. In addition to these general moisture requirements, there are 
certain sequences of climatic conditions necessary for the production 
of the species in large numbers, which must be fulfilled in any season 
before an outbreak can occur. The temperature relations of C. unt- 
puncta during the fall and winter months are an example of such a 
condition. 

4. Of these conditions, those surrounding hibernation seem to he 
of the greatest importance, and an outbreak seems to be directly related 
to the percentage of the larvae that survive the winter successfully. 


METEOR@EOGICAL] RELATIONS OH Eb eA 1D UTe Devi iis 


As was already stated, the data relating to the effects of weather 
conditions on moth flight were secured at St. Paul, Minn., in 1920, 
and at Havre, Mont., in 1921. The Minnesota data were published in 
a former paper (Cook ’21) together with a part of the present statist- 
cal treatment, and these basic data will not be repeated here. 

Bait traps were run at Havre between August 1 and September 5, 
when a cold wave and considerable snowfall practically put an end to 
moth flight. The traps used were large glazed earthenware receptacles 
holding about five gallons each. Eleven of these were used during the 
height of the flight season on two fields, being placed about three 
hundred feet apart and about three feet above the ground. The bait 
used was a 10 per cent solution (by volume) of crude beet molasses, 
obtained from the Great Western Sugar Co., at Billings, Mont. 
Because of the high evaporation it was found necessary to renew the 
solution about twice a week. 

A record was kept of the numbers caught of each of the more 
abundant species per night, and a comparative count of the males and 
females of Porosagrotis orthogonia, which was the species on which 
the most accurate data were desired. As the catches for a few nights 
at the height of the flight period were too large to be counted by one 
individual, the entire catch was preserved for each night by drying, 
and later counted by the following method of sampling. The entire 
night’s catch was placed in a conical pile on a flat surface, and 
separated by planes through the apex into a series of radiating piles, 
each of which represented a definite fraction of the catch (one-fourth 
or one-eighth, depending on the size of the total catch). One of these 
piles was then carefully examined and sorted, and the rest of the catch 


Hares 
Ly 


PHYSICAL ECOLOGY OF THE NOCTUIDAE 31 


inerely counted, the total for each species being assigned pro rata from 
the proportion found in the examination of the fraction. This method 
was found to give results of relatively high accuracy. 

Table XII gives the total figures for the more abundant Noctuids, 
obtained as described above. 


TABLE XII 


Motu FLIGHT AT HAVRE, MONT. 
AUGUST 1 TO SEPTEMBER 8, 1921 


No. of Per cent of 

Species specimens total catch 
Porosagrotis orthogonia......... Males 6,450 10.8 
Females 14,614 24.5 
FULOG PAA Pennisi . 5. ace bh chs oo 28,309 47.2 
EuUNoG -CuUadridentald Fan . oc 4 chiseled 2,826 4.7 
DEDCMIAGEVASEALON On 6 euev ea re we DISYGW 4.3 
CarGdrinag Cxlima ca 6 oo ok ek Poe 681 14 
Other speciedie cat, oti eee ote te te 4,640 7.4 
Total 60,057 100.0 


*Included in this record are E. quadridentata, E. dargo, E. ridingsiana, and several other 
closely related species. 


Included among the “other species” were Chorizagrotis auxiliarts, 
Feltia ducens, Porosagrotis catenula, and about twenty-five other 
species, mostly of the genus Euxoa, as well as considerable unidenti- 
fiable material. None of these species was present in more than one 
per cent of the total. 

The noteworthy feature of the catch was the great and increasing 
abundance of Euroa pallipennis, a species formerly very rare, but at 
present the most common single species. So far as is known, the 
species is not injurious to crops, but the larva has not been positively 
identified. 

Records of temperature and humidity were available at the 
experiment station from instruments exposed to field conditions within 
half a mile of the traps. Pressure observations taken at 6:00 p. m. 
were obtained from Mr. C. M. Ling, United States Meteorologist at 
Havre, about seven and one-half miles distant. As pressure varies 
rather slowly, these readings gave a good index to conditions at the 
station. The data for catches, temperature, humidity, pressure, and 
precipitation, together with the five-day sliding average for each, com- 
puted as in the former page, are given in Table XIII. The normals, 
which were not computed for the weather factors in the Minnesota 
data as published, were also computed for these factors, but the 
figures are not included. Plate V is a graphical representation of 
Table XIII. For each factor are shown a straight line representing 
the seasonal mean, an angular graph showing the daily variations in 
the factor, and a smoother curve closely approximating the five-day 
normals. 


» ~ me: 
v v ¥ re »: 
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(91) (ST) (FI) (€T) (ZT) (TT) (OT) (6) (8) (L) (9) (S$) (r) (€) (Z) (T) 
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(A) Nochurds Gapturdd 
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othe 
pee jh is BE “ ips hee 
Vor th KT Per, 


lempekalare |7i1™ 


Plate V. Meteorological Relations of Adult Moths 


Figure 14. 

(a) Number of Noctuids caught per trap per night at Havre, Mont., 
from August 1 to September 8, 1921. 

(b) Temperature at 7 p. m. 

(c) Relative humidity at 7 p. m. 

(d) Barometric pressure at the United States Weather Bureau Station 
at Havre, taken at 6 p. m. 


34 TECHNICAL BULEELIN Wz 


METHODS, QF STATISTICAL ANALYSIS 

In the first place, the object in computing the five-day normal 
catch was to reduce the figures for the catch from the widely vary- 
ing daily figures to a common denominator, a percentage, or index 
number. Then similar normals were computed for the other factors 
for the sake of uniformity in treatment as well as for the elimination 
of any long-period trends. (Yule, 19, p. 200). Having these three 
figures for each factor, we have at our disposal three different 
methods of statistical treatment, which will bring out the facts from 
three entirely different angles. For example, a study of the relations 
between the index catch and the observed values of weather factors 
will show which particular values of those factors, if any, are most 
favorable to moth flight. Then, a further study of the relation 
between the variations in these factors and the variations in the catch 
will bring out any relationship between a change in any factor and the 
catch. Finally, a study of the relation between the departure of the 
normal catch from the season average and ‘the departures of the 
weather factor normals from their season averages, will show the 
relationship, if any, which exists between the emergence of the various 
species and the condition of the weather during the period of 
emergence. All three of these methods of analysis have been applied 
to both sets of data, and partial correlations worked out between the 
catch factor and the various weather factors. These coefficients, 
obtained in the manner explained in the previous paper, are all given 
in Table XIV, on the opposite page. The coefficients are divided into 
three groups, indicated by the designations A, B, and C, corresponding 
to the three methods of analysis outlined above. 

The coefficients of group A, which are the ones published for the 
Minnesota data in the previous paper, are intended as a measure of 
the relationship between the index catch and the observed values of 
the weather factors. It was found necessary to divide the Minnesota 
data on the basis of humidity, the dividing lines being below 54 per 
cent and above 50 per cent respectively. The same process was 
necessary in treating the Montana data, except that the dividing line 
in this case was drawn below 40 per cent and above 30 per cent. 
Humidity is the most significant factor in this group, and the largest 
index catches were secured in times when this factor was near the 
mean for the season. In other words, the moths flew best in times 
when humidity was about average for the season. None of the 
coefficients is large, and the Montana figures would be of little value 
except that they show the same tendency as the Minnesota figures. 


4 


wa 


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$10}0eY = 
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(IIIX ATAVL ‘ET ‘OT *£ ‘9 SNWNTOD) 
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SUYOLOVY TVOIDOIONOALAJY HLIM LHDITY HLOJY AO SNOILVIANNOD 
AIXPA TS VL 


36 TECHNICAL BULLCETING? 


Considering the coefficients of Group B, we have a much different 
condition. In this set of correlations, the effects of variations in the 
factors were studied, and variations in humidity have the smallest 
effect of any factor studied. Temperature and pressure both have 
significant positive correlations, which may be interpreted as follows: 
When the temperature and pressure are higher, and the humidity 
lower, on any particular night than the averages of these factors for 
the five nights.of which this one is the center, then the catch is also 
higher than the average for these five nights. That is, moths fly more 
freely on warm, dry nights, following cooler, damper nights than when 
the reverse is true. 

It is in group C that the largest values are found for the correla- 
tion coefficients. As the figures correlated are averages for five-day 
periods, the relations must be considered as being relations of the 
weather factors to emergence. Thus, under Minnesota conditions, 
more moths emerge in a time of higher temperature and lower pres- 
sure and higher humidity than the season average, the humidity being 
the most important factor, followed by temperature and pressure. In 
the Montana data temperature was of practically no significance, but 
there was a very high relationship between emergence and the other 
two factors, with humidity slightly more important. Evidently, more 
moths emerge in times of high humidity in humid regions, and more 
moths emerge in times of low humidity in arid regions. The size of 
the coefficient of multiple correlation in the latter case, “R’==+ .92, 
indicates that the emergence of moths in the arid regions is almost 
entirely a function of these climatic conditions. 

To summarize these relations; the observed values of humidity 
have an important bearing on the flight of moths, the largest numbers 
flying when the humidity is near the seasonal mean. Humidity also 
affects emergence, more emerging under high humidity conditions in 
Minnesota and under low humidity conditions in Montana. Varia- 
tions in temperature and pressure from night to night are of more 
importance than variations in humidity. Further studies, and the 
accumulation of more data may affect these relationships, but probably 
will only intensify them. 


CDN C EGS LONG 


A general consideration of the studies presented in this paper leads 
to the following conclusions: 

1. Each of the species included in this study has a very definite 
optimum soil moisture requirement, which, broadly speaking, limits 
the distribution of the species. 


¢) 


\ 


PHYSICAL ECOLOGY OF THE NOCTUIDAE 37 


2. This requirement may be determined experimentally under 
controlled conditions, and also indirectly, by a statistical analysis of 
the weather conditions surrounding outbreaks of that species. 

3. In each case, the optimum moisture requirement of the species 
which occur in any given region is a close approach to the normal 
climatic condition in that region, so that outbreaks would occur every 
season were it not that there is also a necessary seasonal sequence of 
conditions which must be fulfilled in order to enable the insect to 
reach destructive abundance. 

4. This sequence, which may operate either by favoring the 
destructive insect, by limiting the activities of its enemies, or both, 1s 
the controlling factor in the production of outbreaks, and a careful 
study of such a sequence in the life history of any insect should enable 
us to predict the possibility of an outbreak of that insect in any given 
region. 

In conclusion, the writer wishes to emphasize the importance of 
the use of mathematical methods in the study of insect outbreaks, as 
well as to show its practical application in the examples cited. As the 
literature of statistics is rather foreign to entomological workers, a 
few selected titles of especially valuable works, which are of great 
service in such a study, are listed in the bibliography. 


BIBLIOGRAPHY 
REFERENCES ON STATISTICAL METHODS 

Ball, John. Climatological diagrams. Cairo Scientific Journal, Vol. iv, No. 50. 
(First use of the Climograph.) 1910. 

landers, V. B. The Use of Charts and Graphs in the study of climate. Mo. 
Weather Rev. 50:481-484. Sept., 1922. 

Leland, Ora Miner. Practical least squares. McGraw-Hill Book Co., N. Y. 
1921. 


Lipka, Joseph. Graphical and Mechanical Computation. Part I. Alignment 
charts, Part IJ. Experimental Data. John Wiley and Sons, N. Y. 1921. 

Smith, J. Warren. Agricultural Meteorology. Macmillan, N. Y. Rural Text- 
book Series. 1920. 


Varney, B. M. Some further uses of the climograph. U. S. monthly weather 
review, Vol. xlviii, No. 9, pp. 495-497. 1920. 
Yule, G. Udny. An introduction to the theory of statistics. Fifth Edition. 


London, Charles Griffin and Co., Ltd. 1919. 
LITERATURE CITED OTHER THAN STATISTICAL 

Barrett, Charles G. The Influence of Meteorological Conditions on Insect Life. 
Ent. Mo. Mag., Vol. xix, pp. 1-8. 1882. 

Cook, William C. Studies on the Flight of Nocturnal Lepidoptera. 18th Rept 
State. Ent. Minn. for 1920, pp. 43-56. St. Paul. 1921. 

Cooley, Robert A. Observations on the Life History of the Army Cutworm 
Chorizagrotis auxiliaris. Jour. Agr. Res., Vol. vi, No. 23, p. 871-881. 1916 

Criddle, Norman. Precipitation in Relation to Insect Distribution. (Popula: 
and Practical Entomology) Can, Ent., Vol. xlix, No. 3, p. 77-80. 1917. 


38 TRG NICAL SGA T shims 


Fitch, Asa. Sixth Report. on the Insects of New York, p. 121. (Weather and 
the Army Worm.) 1860. 

Folsom, Justus Watson. Entomology with Special Reference to its Biological 
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BIOGRAPHY 


William Carmichael Cook, son of Guy Reuben Cook and Ellen 
Ilizabeth Cook, was born at Syracuse, New York, October 2, 1895. 
lle attended the public schools of Syracuse, graduating from Central 
High School in 1913. He attended the Agriculture College at Syracuse 
University from 1913 to 1916, and the same at Cornell University 
during 1916 and 1917, receiving the B.S. degree at Cornell in 1917. 

During the summer of 1917 he did field work for the Entomology 
Department of Pennsylvania State College. From 1919 to 1922 he did 
graduate work in entomology and insecticide chemistry at the Unt- 
versity of Minnesota, doing field work with the State Entomologist 
during the summer seasons. He received his M.S. in 1920. Since 
May 1, 1921, he has been in the employ of the Montana Experiment 
Station, completing his graduate work on leave of absence in 1922. 

He was married to Muriel M. Amidon, of St. Paul, Minnesota, on 
July 22, 1920. 


Previous publications: 
1920. Cut worms and army worms. Cir. 52, State Ent. Minn. 
1921. Studies on the flight of noctiirnal lepidoptera. 18th 
Rept. St. Ent. Minn. pp. 43-506. 


FINO 


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